We know that not getting enough sleep is not good for us, but on the flipside, getting too much sleep may not be the tonic that our sleep-deprived society is craving. Though scientists are still exploring the strange phenomenon of overdoing it on sleep, early stage research the Journal of the American College of Cardiology shows it may come with its own long term health risks.
The ideal amount of sleep per night changes with age, but the National Sleep Foundation suggests 7-9 hours for young adults, and 7-8 hours for older adults. The new study, published Tuesday, suggests that when we stray too far from that sweet spot, either through sleep deprivation or by oversleeping, the risk of heart attack increases.
In this study, “long sleepers,” or people who sleep more than 9 hours per night, raised their risk of heart attack by 34 percent compared to those who slept between 6 and 9 hours per night. “Short sleepers,” or people who slept for less than 6 hours per night, raised their risk by 20 percent.
These results may sound surprising. Céline Vetter, Ph.D., an associate professor at the University of Colorado Boulder and study co-author, agrees with that assessment: “the long sleep duration part is indeed counterintuitive,” she tells Inverse.
But her paper shows good evidence that just like sleep deprivation, overdoing it on sleep also has heart risks.
The Risks of Too Much (or Too Little) Sleep
Vetter and her colleagues compared the heart disease risk of adults aged 40-69 who slept for either 4, 5, 6, 7, 8, 9, 10, or 11 hours per night. After controlling for variables like BMI and smoker status (lifestyle factors that impact heart disease risk) heart disease risk increased for people who slept 4, 5, 10 or 11 hours per night, but not those who slept between 6 and 9.
And the further people got from that 6-9 hours of sleep, the worse their risks got.
For example, after adjusting for several variables, people who slept for 5 hours per night had 19 percent greater risk of heart attack compared to someone who slept for 7-8 hours regularly. But those who slept 4 hours had 34 percent greater risk.
That pattern was the same on the opposite side of the sleep spectrum, too. People who slept for 10 hours had 32 percent greater risks of a heart attack, and those who slept for 11 hours had 87 percent higher risks.
On the sleep-deprived side of things, these results fit with well-established connections between sleep deprivation and heart conditions. But when it comes to the long sleep end of the equation, things are a bit murkier. It’s still unclear why there are heart risks associated with long sleeping and what we should do about them.
Why Is Overdoing It on Sleep Risky?
Vetter explains that there is a number of observational studies that, like hers, demonstrate that sleeping too much may have negative effects.
In August 2018, an analysis of 74 studies published in the Journal of the American Heart Association showed that patients who consistently slept for 10 hours per night had a 30 percent increase in risk of death and a 49 percent increase in cardiovascular disease-related death.
Still there aren’t many explanations for why long-duration sleep is risky. One idea is that oversleeping is just a marker of another condition that might be contributing to poor health or heart disease. When that 2018 study came out, Brooke Aggarwal, Ph.D., a behavioral scientist and clinical health education specialist at Columbia University Medical Center, told Inverse that sleeping too much may be a warning sign of poor health, but not necessarily risky in itself.
“I think that longer sleep could be a ‘red flag’ or early marker of an underlying medical issue, which highlights the importance of asking about sleep at physician visits in order to identify individuals who may be at increased risk for cardiovascular disease and mortality,” she told Inverse.
Vetter, the author of this most recent study, agrees that this idea is still relevant.
“One hypothesis how this was explained was that long sleep is basically a sign of poor health, and that these individuals must be more depressed, and sicker,” says Vetter.
But to address whether the long sleepers were just more likely to be in poor health for other reasons, she and her co-authors looked specifically at healthy people in this sample — they and still found a powerful effect.
“We see that even when we account for a wide range of these conditions, and restrict our sample to individuals without cardiovascular risk factors (no smokers, no overweight/obese individuals, etc), these results persist,” says Vetter.
This doesn’t exactly disprove the hypothesis that long sleepers are suffering from other conditions that may be impacting heart disease risk. But it does suggest that oversleeping may have a unique effect on heart conditions that may not even be clear right now.
“There is some indication that long sleep duration is associated with higher inflammation, a risk factor for heart disease,” says Vetter. “But because we cannot make individuals sleep ‘habitually longer’ in the laboratory, it is hard to study the underlying mechanisms.”
For now, researchers are working with a pattern that only has gotten stronger with Vetter’s results. Going forward, she’s working under a grant from the National Institutes of Health to explore what happens to the heart when we sleep too little. But perhaps even more crucially, she’ll have to uncover what happens when we sleep too much.
Background: Observational studies suggest associations between extremes of sleep duration and myocardial infarction (MI), but the causal contribution of sleep to MI and its potential to mitigate genetic predisposition to coronary disease is unclear.
Objectives: This study sought to investigate associations between sleep duration and incident MI, accounting for joint effects with other sleep traits and genetic risk of coronary artery disease, and to assess causality using Mendelian randomization (MR).
Methods: In 461,347 UK Biobank (UKB) participants free of relevant cardiovascular disease, the authors estimated multivariable adjusted hazard ratios (HR) for MI (5,128 incident cases) across habitual self-reported short (<6 h) and long (>9 h) sleep duration, and examined joint effects with sleep disturbance traits and a coronary artery disease genetic risk score. The authors conducted 2-sample MR for short (24 single nucleotide polymorphisms) and continuous (71 single nucleotide polymorphisms) sleep duration with MI (n = 43,676 cases/128,199 controls), and replicated results in UKB (n = 12,111/325,421).
Results: Compared with sleeping 6 to 9 h/night, short sleepers had a 20% higher multivariable-adjusted risk of incident MI (HR: 1.20; 95% confidence interval [CI]: 1.07 to 1.33), and long sleepers had a 34% higher risk (HR: 1.34; 95% CI: 1.13 to 1.58); associations were independent of other sleep traits. Healthy sleep duration mitigated MI risk even among individuals with high genetic liability (HR: 0.82; 95% CI: 0.68 to 0.998). MR was consistent with a causal effect of short sleep duration on MI in CARDIoGRAMplusC4D (Coronary ARtery DIsease Genome wide Replication and Meta-analysis plus Coronary Artery Disease Genetics Consortium) (HR: 1.19; 95% CI: 1.09 to 1.29) and UKB (HR: 1.21; 95% CI: 1.08 to 1.37).
Conclusions: Prospective observational and MR analyses support short sleep duration as a potentially causal risk factor for MI. Investigation of sleep extension to prevent MI may be warranted.